Sublimation reducing cathode connector



July 15, 1958 D. R. KERSTETTER ETAL 2,843,781

SUBLIMATION REDUCING CATHODE CONNECTOR Filed NOV. 1, 1954 l8 |6 ALUMINUML ALLOY INVENTORS WLLIAM E. BUESCHER JAMES J. GARRETT DONALD R. KERSTETTER BY ATTORNEY United States Patent SUBLIMATION REDUCING CATHODE CONNECTOR Donald R. Kerstetter, William E. Buescher, and James J. Garrett, Emporium, Pa., assignors to Sylvania Electric Products Inc., a corporation of Massachusetts Application November 1, 1954, Serial No. 465,785

1 Claim. (Cl. 313178) This invention relates to method and means for reducing sublimation in thermionic tubes.

It has been found, that in the manufacture and use of thermionic tubes certain deposits formed about the cathode as on the insulating spaces holding the electrodes apart. These deposits it was found are conductive and after a time become heavy enough to afford leakage paths between electrode elements. This impairs the efficiency and reduces the life of the tube. It has been found that these deposits are attributable to the sublimation of the metals of the cathode and cathode tabbing material. The tabbing material serves as the conductor connecting the cathode base to a conductor lead sealed in the tube. During manufacture of the tube, and in use, the cathode is heated to a very high temperature, and so is the tab, the latter by undesired conduction of heat away from the cathode. In common almost universal thermionic tube construction, the supporting body for the electron emissive material, usually the oxides of barium, calcium and strontium, is a nickel alloy containing a high percentage of nickel, well above 90%, a percentage of manganese, about .l0-.20%, and a smaller percentage of other elements as copper, iron and carbon, but a negligible amount, if any, of aluminum.

Usually the tab is also made of a nickel alloy. A common alloy used for the tab is known as D nickel whose nominal composition includes somewhat less than 95% nickel, about 4.65% manganese, and other metals in the range below 1% but, like the supporting body, it contains a negligible amount of aluminum. This material, along with several other materials such as 42% nickel iron alloy, Nilvar, Hastelloy B and others, were selected for this use because of their low thermal conductivity. These specified materials are in common use throughout the tube manufacturing industry. It ap pears that as the manganese of the cathode base sublimes the manganese of the tab may difiuse thereinto to replace the abstracted manganese.

I have discovered that by afi'ixing a certain amount of aluminum or alloy containing this metal to the cathode base alloy, a considerable reduction in the sublimation processes takes place, this reduction being sufficient to eliminate tube losses due to the leakage previously referred to. The aluminum may be added to the cathode in various ways as by spraying or vaporizing the metal or an alloy thereof onto uncoated exterior portions of the cathode or by welding small pieces of aluminum or alloys thereof to the cathode base. Yet another way is by replacing the conventional D nickel tab or other low conductivity materials by a tab containing a quantity of the desired aluminum as for example by welding Duranicke tabs to the cathode. An added advantage from the use of aluminum containing tabs is that sublimation from the tabs themselves is materially reduced. Duranicke is a composition containing about 4.00% to 4.75% of aluminum and vaporizes very little under the heat to which it is subject in a thermionic tube. It has been found in practice that the mere substitution of the Duranickel tab for the nickel tabs conventionally used has been sufficient to materially minimize the undesirable sublimation characteristics heretofore described both from the cathode base and the tab and to minimize sublimation depositions to such an extent as not to impair the characteristics of the tube throughout the life of the tube. Furthermore, the substitution of the Duranickel tab for the D nickel tab has permitted the use of wider tabs thereby reducing the inductance of the tab and improving the characteristics of the tube. This is so because the thermo-conductivity of Duranickel is very much smaller than that of the nickel tabs conventionally employed. The larger size of tab is made possible because the use of the aluminum carrying metal alloy does not entail increasing the amount of cathode end cooling. End cooling is objectionable since its lowers the overall cathode temperature and results in lower emission and deterioration of radio tube electrical characteristics. It has been found in practice that the diffusion of the aluminum of the tab into the cathode base is inversely proportional to the distance away from the point of connection of the tab to the cathode base. For satisfactory results the cathode tab should be welded, as is the common practice, to the cathode base, and the percentage of aluminum in the tab should be about 4. However, it has been found that percentages as low as 1% of aluminum in the tab has worked satisfactorily. The upper limit is fixed by the melting point of the aluminum alloy. For example considering aluminum-nickel alloys, the melting point of the alloy does not fall below 1400 C. (except for a small area around 15% aluminum) until the aluminum content is greater than 47%. Where aluminum alloys are welded to uncoated portions of the cathode base they also may have the same composition as the tabs.

The accompanying drawing illustrates an example of a cathode constructed in accordance with the present invention. In this drawing, 10 indicates a nickel alloy sleeve coated at 12 with the oxides of barium, calcium and strontium, there being spaces 14 and 16 above and below the coated area for the application of squares of aluminum bearing alloy as for example is shown at 18. Also, if desired, or in the alternative, the cathode may be tabbed with a tab 20, this tab containing about 4% of aluminum as set forth in the above specification. The cathode sleeve itself is made of the nickel alloy hitherto described but which does not contain any aluminum therein.

A method is herein involved in which cathode alloy material devoid of the metals to suppress sublimation may have such metals supplied to the material after fabrication of the material into a cathode emissive material support.

Having thus described the invention what is claimed as new is:

A cathode base comprising an alloy comprised principally of a large percentage of nickel and a much smaller percentage of manganese with insignificant traces of other metals, an electron emissive coating on said base, and a nickel alloy cathode tab with a content of, approximately, 4% of aluminum permanently secured to an uncoated end of said cathode base.

References Cited in the file of this patent UNITED STATES PATENTS 1,724,465 Engels Aug. 13, 1929 1,952,428 Forst Mar. 27, 1934 2,103,031 Foulke Dec. 21, 1937 2,123,686 Spencer July 12, 1938 2,206,504 Kinycn July 2, 1940 2,206,937 Briggs July 9, 1940 2,444,158 Driggs June 29, 1948 2,556,254 Carne June 12, 1951 

